arm_ffa: introduce Arm FF-A support

Add Arm FF-A support implementing Arm Firmware Framework for Armv8-A v1.0

The Firmware Framework for Arm A-profile processors (FF-A v1.0) [1]
describes interfaces (ABIs) that standardize communication
between the Secure World and Normal World leveraging TrustZone
technology.

This driver uses 64-bit registers as per SMCCCv1.2 spec and comes
on top of the SMCCC layer. The driver provides the FF-A ABIs needed for
querying the FF-A framework from the secure world.

The driver uses SMC32 calling convention which means using the first
32-bit data of the Xn registers.

All supported ABIs come with their 32-bit version except FFA_RXTX_MAP
which has 64-bit version supported.

Both 32-bit and 64-bit direct messaging are supported which allows both
32-bit and 64-bit clients to use the FF-A bus.

FF-A is a discoverable bus and similar to architecture features.
FF-A bus is discovered using ARM_SMCCC_FEATURES mechanism performed
by the PSCI driver.

Clients are able to probe then use the FF-A bus by calling the DM class
searching APIs (e.g: uclass_first_device).

The Secure World is considered as one entity to communicate with
using the FF-A bus. FF-A communication is handled by one device and
one instance (the bus). This FF-A driver takes care of all the
interactions between Normal world and Secure World.

The driver exports its operations to be used by upper layers.

Exported operations:

- ffa_partition_info_get
- ffa_sync_send_receive
- ffa_rxtx_unmap

Generic FF-A methods are implemented in the Uclass (arm-ffa-uclass.c).
Arm specific methods are implemented in the Arm driver (arm-ffa.c).

For more details please refer to the driver documentation [2].

[1]: https://developer.arm.com/documentation/den0077/latest/
[2]: doc/arch/arm64.ffa.rst

Signed-off-by: Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Jens Wiklander <jens.wiklander@linaro.org>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>

2 files changed, 239 insertions, 0 deletions

diff --git a/doc/arch/arm64.ffa.rst b/doc/arch/arm64.ffa.rst
new file mode 100644
index 0000000..4f817f0
--- /dev/null
+++ b/doc/arch/arm64.ffa.rst
@@ -0,0 +1,238 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Arm FF-A Support
+================
+
+Summary
+-------
+
+FF-A stands for Firmware Framework for Arm A-profile processors.
+
+FF-A specifies interfaces that enable a pair of software execution environments aka partitions to
+communicate with each other. A partition could be a VM in the Normal or Secure world, an
+application in S-EL0, or a Trusted OS in S-EL1.
+
+The U-Boot FF-A support (the bus) implements the interfaces to communicate
+with partitions in the Secure world aka Secure partitions (SPs).
+
+The FF-A support specifically focuses on communicating with SPs that
+isolate portions of EFI runtime services that must run in a protected
+environment which is inaccessible by the Host OS or Hypervisor.
+Examples of such services are set/get variables.
+
+The FF-A support uses the SMC ABIs defined by the FF-A specification to:
+
+- Discover the presence of SPs of interest
+- Access an SP's service through communication protocols
+  e.g. EFI MM communication protocol
+
+At this stage of development only EFI boot-time services are supported.
+Runtime support will be added in future developments.
+
+The U-Boot FF-A support provides the following parts:
+
+- A Uclass driver providing generic FF-A methods.
+- An Arm FF-A device driver providing Arm-specific methods and reusing the Uclass methods.
+
+FF-A and SMC specifications
+-------------------------------------------
+
+The current implementation of the U-Boot FF-A support relies on
+`FF-A v1.0 specification`_ and uses SMC32 calling convention which
+means using the first 32-bit data of the Xn registers.
+
+At this stage we only need the FF-A v1.0 features.
+
+The FF-A support has been tested with OP-TEE which supports SMC32 calling
+convention.
+
+Hypervisors are supported if they are configured to trap SMC calls.
+
+The FF-A support uses 64-bit registers as per `SMC Calling Convention v1.2 specification`_.
+
+Supported hardware
+--------------------------------
+
+Aarch64 plaforms
+
+Configuration
+----------------------
+
+CONFIG_ARM_FFA_TRANSPORT
+    Enables the FF-A support. Turn this on if you want to use FF-A
+    communication.
+    When using an Arm 64-bit platform, the Arm FF-A driver will be used.
+
+FF-A ABIs under the hood
+---------------------------------------
+
+Invoking an FF-A ABI involves providing to the secure world/hypervisor the
+expected arguments from the ABI.
+
+On an Arm 64-bit platform, the ABI arguments are stored in x0 to x7 registers.
+Then, an SMC instruction is executed.
+
+At the secure side level or hypervisor the ABI is handled at a higher exception
+level and the arguments are read and processed.
+
+The response is put back through x0 to x7 registers and control is given back
+to the U-Boot Arm FF-A driver (non-secure world).
+
+The driver reads the response and processes it accordingly.
+
+This methodology applies to all the FF-A ABIs.
+
+FF-A bus discovery on Arm 64-bit platforms
+---------------------------------------------
+
+When CONFIG_ARM_FFA_TRANSPORT is enabled, the FF-A bus is considered as
+an architecture feature and discovered using ARM_SMCCC_FEATURES mechanism.
+This discovery mechanism is performed by the PSCI driver.
+
+The PSCI driver comes with a PSCI device tree node which is the root node for all
+architecture features including FF-A bus.
+
+::
+
+   => dm tree
+
+    Class     Index  Probed  Driver                Name
+   -----------------------------------------------------------
+   ...
+    firmware      0  [ + ]   psci                      |-- psci
+    ffa                   0  [   ]   arm_ffa               |   `-- arm_ffa
+   ...
+
+The PSCI driver is bound to the PSCI device and when probed it tries to discover
+the architecture features by calling a callback the features drivers provide.
+
+In case of FF-A, the callback is arm_ffa_is_supported() which tries to discover the
+FF-A framework by querying the FF-A framework version from secure world using
+FFA_VERSION ABI. When discovery is successful, the ARM_SMCCC_FEATURES
+mechanism creates a U-Boot device for the FF-A bus and binds the Arm FF-A driver
+with the device using device_bind_driver().
+
+At this stage the FF-A bus is registered with the DM and can be interacted with using
+the DM APIs.
+
+Clients are able to probe then use the FF-A bus by calling uclass_first_device().
+Please refer to the armffa command implementation as an example of how to probe
+and interact with the FF-A bus.
+
+When calling uclass_first_device(), the FF-A driver is probed and ends up calling
+ffa_do_probe() provided by the Uclass which does the following:
+
+    - saving the FF-A framework version in uc_priv
+    - querying from secure world the u-boot endpoint ID
+    - querying from secure world the supported features of FFA_RXTX_MAP
+    - mapping the RX/TX buffers
+    - querying from secure world all the partitions information
+
+When one of the above actions fails, probing fails and the driver stays not active
+and can be probed again if needed.
+
+Requirements for clients
+-------------------------------------
+
+When using the FF-A bus with EFI, clients must query the SPs they are looking for
+during EFI boot-time mode using the service UUID.
+
+The RX/TX buffers are only available at EFI boot-time. Querying partitions is
+done at boot time and data is cached for future use.
+
+RX/TX buffers should be unmapped before EFI runtime mode starts.
+The driver provides a bus operation for that called ffa_rxtx_unmap().
+
+The user should call ffa_rxtx_unmap() to unmap the RX/TX buffers when required
+(e.g: at efi_exit_boot_services()).
+
+The Linux kernel allocates its own RX/TX buffers. To be able to register these kernel buffers
+with secure world, the U-Boot's RX/TX buffers should be unmapped before EFI runtime starts.
+
+When invoking FF-A direct messaging, clients should specify which ABI protocol
+they want to use (32-bit vs 64-bit). Selecting the protocol means using
+the 32-bit or 64-bit version of FFA_MSG_SEND_DIRECT_{REQ, RESP}.
+The calling convention between U-Boot and the secure world stays the same: SMC32.
+
+Requirements for user drivers
+-------------------------------------
+
+Users who want to implement their custom FF-A device driver while reusing the FF-A Uclass can do so
+by implementing their own invoke_ffa_fn() in the user driver.
+
+The bus driver layer
+------------------------------
+
+FF-A support comes on top of the SMCCC layer and is implemented by the FF-A Uclass drivers/firmware/arm-ffa/arm-ffa-uclass.c
+
+The following features are provided:
+
+- Support for the 32-bit version of the following ABIs:
+
+    - FFA_VERSION
+    - FFA_ID_GET
+    - FFA_FEATURES
+    - FFA_PARTITION_INFO_GET
+    - FFA_RXTX_UNMAP
+    - FFA_RX_RELEASE
+    - FFA_RUN
+    - FFA_ERROR
+    - FFA_SUCCESS
+    - FFA_INTERRUPT
+    - FFA_MSG_SEND_DIRECT_REQ
+    - FFA_MSG_SEND_DIRECT_RESP
+
+- Support for the 64-bit version of the following ABIs:
+
+    - FFA_RXTX_MAP
+    - FFA_MSG_SEND_DIRECT_REQ
+    - FFA_MSG_SEND_DIRECT_RESP
+
+- Processing the received data from the secure world/hypervisor and caching it
+
+- Hiding from upper layers the FF-A protocol and registers details. Upper
+  layers focus on exchanged data, FF-A support takes care of how to transport
+  that to the secure world/hypervisor using FF-A
+
+- FF-A support provides driver operations to be used by upper layers:
+
+    - ffa_partition_info_get
+    - ffa_sync_send_receive
+    - ffa_rxtx_unmap
+
+- FF-A bus discovery makes sure FF-A framework is responsive and compatible
+  with the driver
+
+- FF-A bus can be compiled and used without EFI
+
+Example of boot logs with FF-A enabled
+--------------------------------------
+
+For example, when using FF-A with Corstone-1000 the logs are as follows:
+
+::
+
+   U-Boot 2023.01 (May 10 2023 - 11:08:07 +0000) corstone1000 aarch64
+
+   DRAM:  2 GiB
+   Arm FF-A framework discovery
+   FF-A driver 1.0
+   FF-A framework 1.0
+   FF-A versions are compatible
+   ...
+   FF-A driver 1.0
+   FF-A framework 1.0
+   FF-A versions are compatible
+   EFI: MM partition ID 0x8003
+   ...
+   EFI stub: Booting Linux Kernel...
+   ...
+   Linux version 6.1.9-yocto-standard (oe-user@oe-host) (aarch64-poky-linux-musl-gcc (GCC) 12.2.0, GNU ld (GNU Binutils) 2.40.202301193
+   Machine model: ARM Corstone1000 FPGA MPS3 board
+
+Contributors
+------------
+   * Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>
+
+.. _`FF-A v1.0 specification`: https://documentation-service.arm.com/static/5fb7e8a6ca04df4095c1d65e
+.. _`SMC Calling Convention v1.2 specification`: https://documentation-service.arm.com/static/5f8edaeff86e16515cdbe4c6
diff --git a/doc/arch/index.rst b/doc/arch/index.rst
index b8da4b8..2f916f4 100644
--- a/doc/arch/index.rst
+++ b/doc/arch/index.rst
@@ -8,6 +8,7 @@ Architecture-specific doc
 
    arc
    arm64
+   arm64.ffa
    m68k
    mips
    nios2